Miniature precision resistance element



Dec. 17, 1963 E. c. NUNN MINIATURE PREcIsIoN RESISTANCE ELEMENT Filed June 29. 1961 ITI 24 FIE' E? 55 Aff/5:27! Univ... A l i..

4/ INVENTOR.

Fav/1v I /Vwwv BY @La CALM- 4 froze/vers United States Patent O 3,114,890 MlNlATURE PRECISUN RESliSTANE ELEMENT )Edwin C. Nunn, Fridley, Minn., assigner to Minco Products, Inc., Minneapolis, Minn., a corporation of Minnesota lliied .lune 29, 1961, Ser. No. 1211,654 11 Claims. (Cl. 3dS- 270) The present invention is directed to a miniature precision resistance element of peculiar design which incorporates the advantages of a long sensing element with a miniaturized construction.

The fabrication of precision resistance elements for temperature sensing has, for many years, incorporated the use of resistance type wire wound on a support. In most cases the unit, if it is to incorporate any length of wire, has been rather large. Large units of the type found in the prior art are limited in speed of response due to the inherently large mass. In order to accomplish the miniaturization of this type of unit, a means must be found in which to reduce the effective length of the unit and make it stable, shock-resistant, and subject to easy mounting in any position without deterioration or loss of sensitivity. The present invention incorporates both a physical structure available for miniaturizing a temperature sensing resistance element of this type as well as a method of fabricating this type of unit.

The present invention is directed to a temperature sensing element, or thermometer, that is exceedingly small in physical dimensions while providing features found in much larger units. The present unit is approximately 0.138 inch in diameter and 0.4 inch in maximum length excluding the wires connected to the unit. In order to obtain a resistance type thermometer of substantially high resistance, it is necessary to utilize an exceedingly fine wire. The wire in the present invention may be, for example, 0.0007 inch in diameter and may be platinum. The wire may be bare and is coiled and then wrapped about a support in a manner that will be described in detail in the present specification. Approximately four feet of this wire is used in the unit which is much less than one half inch in length. The application of my invention provides improved accuracy and repeatability. Further, it is possible to provide a device having a relatively high impedance and a relatively large resistance change per unit of temperature. In order to help provide a good temperature response and further prevent mechanical damage to the unit, the unit may be sealed in a hermetically sealed container with or without some type of fluid for damping. The fluid fills the space remaining between the mechanical structure and housing and provides good thermal transfer characteristics and clamps the unit against vibrations and shocks. An example of a fluid ll that posseses characteristics useful in this type of installation is a light form of silicone oil.

It is the primary object of the present invention to disclose a miniature precision resistance element that incorporates a rather long, thin wire in a manner that is free of strains and is adequately supported to provide a stable and shock-free type of unit.

1t is a further object of the present invention to disclose a method of fabricating a miniature precision resistance element that can incorporate over four feet of wire in a unit that is less than one half inch in length.

Yet a further object of the present invention is to disclose a hermetically sealed precision resistance temperature sensing element or thermometer that can be mounted in any position by either attaching the unit directly to the surface by an adhesive, which may be thermally conductive, or by mounting the unit in condition sensing relationship with an area or volume using suitable mounting means.

3,114,890 Patented Dec. 17, 1963 Cice Yet another object of the present invention is to disclose a miniature resistance element that is exceedingly accurate and has Very repeatable characteristics.

Another object of this invention is to provide a versatile device in which a plurality of conductors may be suitably connected to various resistance determining devices and wherein such conductors contribute to the mechanical stability of the unit.

Still a further object of the present invention is to disclose a resistance element that can be made up either on a solid core or on a core conguration that can be made of laminating insulated discs into a core.

These and other objects will become apparent when the drawings are considered in conjunction with the present specification.

FlG. 1 is a cross section of a preferred embodiment of the entire unit.

FIG. 2 is a schematic circuit showing the connections within the present invention.

FG. 3 is an exploded view of a modification of FIG. l in which the core is made up of a number of mica spacers laminated together to form a core construction.

FIG. 4 is a partial cross section of a precision resistance element made up utilizing a core of the type disclosed in FIG. 3.

In FIG. 1 there is disclosed a precision resistance eleient in the form of a resistance thermometer or temperature sensing element for which a cover 10 is provided. The cover 10 may be an extruded or fabricated cap which may, for instance, be of metallic composition of conventional design having an end 11 that is closed and an open end 12.. End 12 is mounted around a metallic header 13 that has sealed therethrough three connection wires 11i, 15 and 16. The header 13 is of a conventional type in which a glass seal is provided between the header 13 and the wires 14, 15 and 16. The header 13 further has a reduced tubular portion 17 that is mechanically attached to the header 13.

Wires 1d, 15 and 16 pass through an insulating disc 20 that can be made up of any material such as mica or ceramic. The disc 2l) is supported by the three wires and acts as a spacer between the bulk of the element and the metal header 13. Further supported by the wires 1d, 1S and 16 is a ceramic core 21 that has a spiral groove 22 either cut or formed into its surface. The groove has a bottom surface 23 that is rounded to accept a resistance element 24;. The resistance element 24 will be described in some detail subsequently. It should be noted that the bottom surface 23 is just broad enough to accept the resistance element 24 without any appreciable binding so that no particular strain is placed on the resistance element.

The core 21 is supported by the wires 14, 15 and 16 passing through its center with the wires coming out of the core on the right end Z5. it will be noted that the wires 14, 15 and 16 are shown at the right end 2.5 of the unit in a slightly bent configuration. Two of the wires, 1S and 1o, are attached to one another by welding or any other convenient process so that a common connection can be removed from the unit for use in a bridge circuit. This point will be well clearly defined in connection with FlG. 2. The core 21 is supported by wires 14, 15 and 16 which support the entire unit within the casing 10. One end of the resistance coil 24 passes into the core 21 at 26 where it passes back through core 21 and is attached to the junction of wires 15 and 16 on the core end 25. The other end of coil 24 is attached at 27 to conductor 14. The arrangement thus provides a single connection on conductor or wire lll to one side of the coil 211 while the conductors 15 and 16 are jointly connected to the other end of the coil 24.

in order to guarantee that the coil of resistance wire 2li,

which is a bare wire of approximately 0.0007 inch in diameter, does not touch the housing l0, an insulated layer of rolled mica or other suitable material, 30 is placed on the inside of the cover i prior to assembly. Wire 24 may be insulated with a suitable insulation in which case insulating layer 30 may be omitted. The cover l0, with its mica insulating insert 30, is sealed at 31 in a hermetic fashion. The seal is accomplished by soldering the unit completely together thereby providing a hermetically sealed can i0. It should be further noted that the void space in the present resistance element may be filled with any convenient fluid prior to sealing. The uid has not been specifically shown in order to avoid a conict of shading with the small details of the coil. The fluid ll may be a fiuid having good thermal transfer properties, viscosity suitable for damping, and dielectric insulating characteristics. A fluid fill would prevent shocks and vibrations as well as improve the temperature response and temperature dissipation properties of the resistance thermometer. A common fluid for this type of arrangement is a lightweight silicone oil.

Prior to discussing the circuit of FIG. 2 or the features of the present invention, it should be noted that a unique method of fabricating the unit disclosed has been evolved. An exceedingly thin wire, which has been set forth as a 0.0007 inch diameter bare platinum wire of nearly four feet in length, is coiled about a thin mandrel. The mandrel in reality is a shaft of thin piano wire and provides a winding form. The thin platinum wire is wound around the mandred until the four foot length is reduced to a resistance coil. The resistance coil 24 is thus developed. Resistance coil 24 is removed from the mandrel and then wound under a slight tension about the spiral core 2l in the bottom surface 23. With this arrangement substantially all of the platinum wire, which makes up the coil 24, is supported over its major length. After the unit disclosed in FIG. l has been assembled, a further method of manufacture is accomplished. A voltage, of approximately 50 volts, is applied to the element between conductors 14 and 15 or I6. The application of a voltage heats coil 24 and allows the coil to be strain relieved. The strain relief process and arrangement of the coil on the core, once completed, has provided the unit with a completely strain-free coil. The voltage applied for temperature aging or strain relief by annealing is gradually removed from the unit by lowering the voltage over a period of time. Once the unit disclosed has cooled, a complete strain relief has been accomplished and the unit is ready for application. Annealing of the unit may be accomplished by other suitable methods.

In FIG. 2 there is disclosed a wiring diagram of the connections to the present unit. The resistance element or coil 24 is shown as having wire I4 connected to one end, while wires 15 and 16 are connected to the other end. The use of three wires to the resistance element or coil 24 allows for the hook-up of the present precision resistance element into a bridge circuit in a fashion will tend to reduce or eliminate losses or unbalances caused by the running of wires from the bridge to the element. It is contemplated that other measuring techniques may lead to the utilization of, for instance, a four conductor configuration in the connection and support wires for the coil 24.

The present invention can be placed on various types of core configuration. It must be appreciated that a core which is less than 0.4 inch in length is rather difficult to build. In order to fabricate a core of an insulated material that will withstand the temperature extremes that the present type of unit must be submitted to, a second embodiment of core configuration is shown. The balance of the invention is substantially the same. That 1s, the core is wrapped with a resistance coil that was first manufactured from a straight resistance wire that was spirally wound around a form or mandrel. In FIG.

3, there is disclosed an exploded view of a core fabricated of a group of mica spacers. A group of spacers 40 are shown which are completely round disc-like rnernbers. These discuike mica members have four holes pierced in them. These four holes allow four wires of relatively large size to be placed through the group to hold them in an assembled relationship. Spaced between equal numbers of the mica discs 40 are a second mica disc lill. The second mica disc 41 is slightly larger than disc 40 and further has a attened side. By providing a larger configuration of the mica disc 4l, it is possible to provide insulating spacers between the balance of surfaces that are built up by the spacers 40. By rotating the spacers 41 ninety degrees at each interval it is possible to form a core, when assembled, that has a passage means that is capable of supporting the resistance coil at its bottom surface and which passage means progresses fully from one end of the core to its other end. Four support wires 42, 43, 44 and 45 form a means not only of holding the core made up of the plurality of spacers 40 and 4l in position, but also provide a means of mounting the core within a resistance element in the same fashion as was disclosed in connection with FIG. l.

FIG. 4 there is disclosed an assembled core in a disclosure which parallels FIG. 1 of the present case. The assembled unit of FIG. 4 is cut away and shows only the left end of an assembled unit. The right end would follow the techniques disclosed in connection with FIG. l. In FIG. 4 there is a header 50 with a reduced portion 51 that mounts the four wires 42, 43, 44 and 45. The four wires pass through the header in a hermetically sealed fashion and are shown supporting the first mica disc 4l that forms an end of the core. A group of mica discs 41 are progressively shown spaced by three smaller discs 40'. The spacing of the discs 4l provides a winding space or passage and by having a flatted side 46 rotated at each ninety degree interval, it is possible to provide a passage means that has an opening between the spacers 41 at 270 degree intervals. -In effect, this arrangement provides an insulated core 52 on-to which a coil of wire 53 has been placed. Again the coil 53 corresponds to the coil 24 of FIG. l. A can or housing 54 is provided around the unit and is sealed at 55 in a hermetic fashion if so desired. The inside of the cover 54 contains a rolled mica insulation material 56 to keep 4the core structure from shorting out against the cover.

The method of fabricating the device disclosed in the FIGS. 3 and 4 is quite similar to that of the device disclosed in lFIG. l. First of all, the core 52 is assembled by placing the mica discs 40 and 41 on the wires 42 to 45. The wires are assembled to the header 50 and are sealed. The resistance coil is wound around the assembled core so that the resistance coil is positioned in a passage means and progresses from one end of the core to the other end. It will be further noted, that the bottom surface of the passage means is of sufficiently broad nature to freely accept the resistance coil without binding. The process of lling the unit with -a temperature dissipating and shock `absorbing fluid can be utilized, as well as the strain relief heating or annealing of the unit.

The present disclosure has been typical of two preferred embodiments of the present invention. While the two preferred embodiments form -a complete `and adequate basis for one skilled in the art to accomplish the present invention, it is obvious that other means of accomplishing the present invention are available. It is understood that suitable modifications may be made in the structure as disclosed, provided such modifications come within the spirit and scope of the appended claims. Having now Itherefore `fully illustrated and described my invention, what I claim to be new and desire to protect by Letters Patent is:

1. A miniature precision resistance element including: a resistance wire spirally wound to form a resistance coil; an insulated core having passage means formed around said core and progressing from one end of said core to its other end; said passage means supporting said resistance coil at `a bottom surface of said passage means so as not to restrict relative movement therebetween; said core further having relatively heavy support wires passing through said core; said support wires passing through header means at one end of said core to hold said core and further provide electrical connection means to said resistance coil; and said header means mechanically holding an insulated and sealed cover on said element to protect and seal said element.

2. A miniature precision resistance temperature sensing element including: a resistance wire spirally wound to form a resistance coil; an insulated core having passage means formed around said core and progressing from one end of said core to its other end; said passage means supporting said resistance coil `at a bottom surface of said passage means; said bottom surface being sufficiently broad to freely accept said resistance coil without binding; said core further having relatively heavy support wires passing through said core; said support wires passing through `a sealed header at one end of said core to hold said core and further provide electrical connection means to said resistance coil; and said header mechanically holding an insulated and hermeticially sealed cover on said element to protect and seal said element.

3. A miniature precision resistance temperature sensing element including: a resistance wire spirally wound to form a resistance coil; an insulated core having passage means formed around said core and progressing from one end of said core to its other end; said passage means supporting said resistance coil at a bottom surface of said passage means; said bottom surface being suiciently broad to freely accept said resistance coil without binding; said core further having relatively heavy support wires passing through said core; said support wires passing through a sealed header at one end of said core to hold said core and further provide electrical connection means to said resistance coil; said header mechanically holding an insulated and hermetically sealed cover on said element; and said element further having a fluid ll to mechanically damp vibrations of said resistance coil and to act as a heat transfer media; said cover and said fluid fill acting to protect and seal said element.

4. A miniature precision resistance element including: a resistance wire spirally wound to form a resistance coil; an insulated core having a spirally formed groove supporting said resistance coil at a bottom surface of said groove so as not to restrict relative movement therebetween; said core further having relatively heavy support wires passing through said core, said support wires passing through header' means at one end of said core to hold said core and further provide electrical connection means to said resistance coil, and said header means mechanically holding an insulated and sealed cover on said element to protect and seal said element.

5. A miniature precision resistance temperature sensing element including: a resistance Wire spirally wound to form a resistance coil; an insulated core having a spirally formed groove supporting said resistance coi-l at a bottom surface of said groove; said bottom surface being dimensioned so as to freely accept said resistance coil without binding; said core further having relatively heavy support wires passing through said core; said support wires passing through a sealed header at one end of said core to hold said core and further provide electrical connection means to said resistance coil; and said header mechanically holding in insulated and hermetically sealed cover on said element to protect and seal said element.

6. A miniature precision ressitance temperature sensing element including: a resistance wire spirally wound to form a resistance coil; an insulated core having a spirally formed groove supporting said resistance coil at a bottom surface of said groove; said bottom surface eing dimensioned so as to freely yaccept said resistance coil without binding; said core further having relatively heavy support wires passing through said core; said support Wires passing Ithrough a sealed header at one end of said core to hold said core and further provide electrical connection means to said resistance coil; said header mechanically holding an insulated and hermetically sealed cover on said element; and said element further having a fluid ll to rnechanically damp vibrations of said resistance coil and to act las a heat transfer media; said cover and said uid fill acting to protect and seal said element.

7. A miniature precision resistance element including: a resistance wire spiral'ly wound to form a resistance coil; a core formed of a plurality of insulated spacers and having passage means formed around said core progressively from one end of said core to its other end; a tirst type of said spacers being disc-like in shape and forming a bottom sur-face for said passage means; a second type of said spacers being larger in diameter than said first type, said second spacers having a fiatted edge and further being placed between said first spacers to form said passage means; said spacers further having relatively heavy support wires passing through said spacers to form said core; said support wires passinT through header means at one end of said core to hold said core and further provide electrical connection means to said resistance coil; and .said header means mechanically holding an insulated and sealed cover on said element to protect and seal said element.

8. A miniature precision resistance temperature sensing element including: a resistance wire spirally wound to form a resistance coil; a core formed of a plurality of Iinsulated spacers and having passage means formed around said core progressively from one end of said core to its other end; a first type of said spacers being disc-like in shape and forming a bottom surface for said passage means; a second type of said spacers being larger in diameter than. said first type; said second spacers having a liatted edge and further being placed between said first spacers to form said passage means; said bottom surface being sufficiently broad to freely accept said resistance coil without binding; said spacers further having relatively lar-ge support wires passing through said spacers to form said core; said support wires passing through a sealed header at one end of said core to hold said core and further provide electr-ical connection means to said resistance coil; and said header mechanically holding an insulated and hermetically sealed cover on said element to protect and seal said element.

9. A miniature precision resistance temperature sensing element including: a resistance wire spirally wound to form a resistance coil; a core formed of a plurality of insulated spacers and having passage means formed around said core progressively from one end of said core to its other end; a first type of said spacers being disclike in shape and forming a bottom surface for said passage means; a second type of said spacers being larger in diameter than said first type; said second spacers having a iiatted edge and further being placed between said first spacers to form said passage means; said bottom surface being sufficiently broad to freely accept said resistance coil Without binding; said spacers further having relatively heavy support wires pasing through said spacers to form said core; said support wires passing through a sealed header at one end of said core to hold said core and further provide electrical connection means to said resistance coil; said header mechanically holding an insulated and hermetically sealed cover on said element; and said e-lement further having a fluid fill to mechanically damp vibrations of said resistance coil and to act as a heat transfer media; said cover and said fluid fill acting to protect and seal said element.

l0. A method of manufacturing a miniature precision temperature sensing element including the steps of winding a bare resistance Wire around a mandrel to form a 7 resistance coil; spirally winding said coil free of said mandrel on an insulated core; anchoring said coil at its ends to conductors which pass through the center of the core and which supports said core; enclosing said core and said coil in `an insulated housing to protect said element; and annealing said element to relieve any strain by connecting said coil through said support Wires to a source of potenti-al to heat said Wire.

11. A method of manufacturing a `miniature precision temperature sensing element including the steps of: Winding a bare resistance wire around a mandrel to form a resistance coil; spirally Winding said coil free of said mandrel on an insulated core; anchor-ing said coil at its ends to conductors ywhich pass through the center of the core and which supports said core; enclosing said core and said coil in an insulated, hermetic housing to protect said element; illing said element with an insulating fluid and annealing said element to relieve any strain by connecting said coil through said support Wires to a source of potential to heat said wire.

References Cited in the file of this patent UNITED STATES PATENTS 995,051 Ayer June 13, 1911 1,134,818 Campbell Apr. 6, 1915 2,287,492 Wood etal. lune 23, 1942 2,780,703 Macintyre Feb. 5, 1957 

1. A MINIATURE PRECISION RESISTANCE ELEMENT INCLUDING: A RESISTANCE WIRE SPIRALLY WOUND TO FORM A RESISTANCE COIL; AN INSULATED CORE HAVING PASSAGE MEANS FORMED AROUND SAID CORE AND PROGRESSING FROM ONE END OF SAID CORE TO ITS OTHER END; SAID PASSAGE MEANS SUPPORTING SAID RESISTANCE COIL AT A BOTTOM SURFACE OF SAID PASSAGE MEANS SO AS NOT TO RESTRICT RELATIVE MOVEMENT THEREBETWEEN; SAID CORE FURTHER HAVING RELATIVELY HEAVY SUPPORT WIRES PASSING THROUGH SAID CORE; SAID SUPPORT WIRES PASSING THROUGH HEADER MEANS AT ONE END OF SAID CORE TO HOLD SAID CORE AND FURTHER PROVIDE ELECTRICAL CONNECTION MEANS TO SAID RESISTANCE COIL; AND SAID HEADER MEANS MECHANICALLY HOLDING AN INSULATED AND SEALED COVER ON SAID ELEMENT TO PROTECT AND SEAL SAID ELEMENT. 